JP3835394B2 - Carbon nanotube production method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a carbon nanotube production method and apparatus for producing carbon nanotubes by an arc discharge method.
[0002]
[Prior art]
A carbon nanotube is a graphene sheet in which carbon atoms are regularly arranged in a hexagonal shape, which is rounded into a cylindrical shape, and has a special physical property, and thus attracts attention as a new material. Such a carbon nanotube may be formed in a deposit aggregated on the carbon electrode side on the cathode side and in a cage-like material scattered around the arc by performing an arc discharge between the two carbon materials. Are known. Various techniques for improving the yield of carbon nanotubes by the arc discharge method have been proposed.
[0003]
For example, when arc discharge is performed in a rare gas, carbon is evaporated and then condensed to form a carbon nanotube, the temperature range of the reaction chamber filled with the rare gas is set to 1000 ° C. to 4000 ° C., and arc discharge is performed. One that produces carbon nanotubes with a uniform distribution of length and diameter is known (see, for example, Patent Document 1).
Further, by covering both the carbon anode and the carbon cathode with a cylindrical carbon heater and performing arc discharge so that the heat radiation temperature of the carbon heater is 500 ° C. to 2000 ° C., Some have increased purity and yield (see, for example, Patent Document 2).
Furthermore, there is a technique in which homogeneous carbon nanotubes can be efficiently generated by heating the tip of an anode made of a carbon electrode and then performing arc discharge (see, for example, Patent Document 3).
[0004]
[Patent Document 1]
JP-A-6-157016 [Patent Document 2]
JP 2000-203820 [Patent Document 3]
JP 2000-344505 A
[Problems to be solved by the invention]
When raising the temperature of the whole reaction chamber like patent document 1, there exists a problem that a manufacturing apparatus becomes complicated.
Further, when only both electrodes or the anode is heated, there is a problem that the synthesis ratio of the carbon nanotubes is low although the consumption amount of the anode electrode is large.
[0006]
The present invention has been made to solve such problems, and it is an object of the present invention to simplify the production apparatus and increase the synthesis ratio of the produced carbon nanotubes.
[0007]
[Means for Solving the Problems]
The carbon nanotube production method according to the present invention synthesizes carbon nanotubes by performing direct current arc discharge using a cathode made of a carbon material, and comprises the entire cathode carbon material or the arc discharge portion of the cathode carbon material. Arc discharge is performed between the anode and the anode after preheating, and the anode is cooled .
[0008]
Further, DC arc discharge is performed while moving the relative position of the cathode and the anode.
[0009]
Further, during the arc discharge, the entire cathode carbon material or the arc discharge portion of the cathode carbon material is heated by a heating means different from the arc discharge.
[0010]
Further, the preheating temperature is set to 500 ° C. to 2000 ° C.
[0011]
Further, the preheating method is characterized by high frequency induction heating, heating by arc discharge or laser irradiation by another electrode, or energization heating by another power source.
[0013]
In addition, the carbon nanotube manufacturing apparatus according to the present invention includes a cathode electrode made of a carbon material, an anode electrode disposed opposite to the cathode electrode at a predetermined interval, and connected to the anode electrode and the cathode electrode. An arc discharge power source for causing arc discharge between these electrodes, a heating means for heating the entire cathode electrode or an arc discharge portion of the cathode electrode, and an anode cooling means for cooling the anode electrode is there.
[0014]
Moreover, the moving means which moves a cathode electrode and an anode electrode relatively is provided.
[0015]
The heating means is a high-frequency induction heating device, an arc discharge device using a separate electrode, or an energization heating device using a laser or a separate power source.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Before describing specific embodiments, the background to the present invention will be described.
The general idea of carbon nanotube synthesis by arc discharge is that carbon vapor and carbon ions generated mainly from the anode carbon electrode diffuse to the cathode side and condense on the surface of the cathode electrode, where the temperature is lower than that of the anode. Multi-walled carbon nanotubes) are synthesized.
Therefore, it is considered that the lower the temperature of the cathode, the faster the growth rate of carbon nanotubes, and the cathode material need not be a carbon material if it is a heat-resistant conductive material.
On the premise of such an idea, increasing carbon vapor and carbon ions from the anode has been considered to greatly contribute to increasing the synthesis ratio of carbon nanotubes.
For this reason, as shown in the conventional example, the entire reaction system or the anode is heated in order to increase the yield of carbon nanotubes.
[0017]
However, according to the experiments of the inventors of the present application, even if only the carbon vapor and carbon ions from the anode are increased, a large amount of graphitic carbon powder or amorphous carbon powder adheres to the cathode surface. Only low ones could be generated.
Therefore, as a result of repeating various experiments, the inventors of the present application have found that the most important factor for increasing the synthesis ratio of carbon nanotubes is not to increase the anode temperature, but the most important factor is to control the temperature of the cathode where the carbon nanotubes are produced. Thus, it was found that maintaining the cathode temperature within an appropriate temperature range is important for producing high-purity carbon nanotubes.
[0018]
The present invention is based on such knowledge, and was born as a result of a change in concept from the conventional focus on only the anode temperature. Hereinafter, specific embodiments of the present invention will be described.
[0019]
Embodiment 1 FIG.
FIG. 1 is a diagram for explaining the configuration of an embodiment of the present invention, and shows the basic configuration of a carbon nanotube production apparatus.
The carbon nanotube manufacturing apparatus according to the present embodiment includes a carbon cathode 1 made of a carbon material, an anode 3 made of a carbon material, a DC power source 5 for generating arc discharge, a cathode preheating means 7 and an anode cooling means 9.
[0020]
The carbon cathode 1 and the anode 3 are arranged with an appropriate gap, and each is connected to a DC power source 5 for generating arc discharge. The carbon cathode 1 and the anode 3 may be placed in a reaction chamber or may be in an air atmosphere outside the container. The cathode heating means 7 may be any one that can preheat or heat the discharge generating portion of the carbon cathode 1 by laser irradiation, such as a YAG laser. The anode cooling means 9 is, for example, water-cooled copper attached in the vicinity of the discharge generating portion of the anode 3 and cools the outer periphery of the anode in the vicinity of the discharge generating portion.
[0021]
Discharge gas supply means (not shown) is provided on the anode side. For example, an inert gas, preferably Ar gas, and a mixed gas containing these gases are discharged from the anode 3 to the cathode 1. In addition, it can be continuously supplied from the anode side toward the cathode side. The discharge generation space here refers to an arc generation space from the anode side to the cathode side. In this way, by continuously supplying the inert gas to the discharge generation space, the ionization degree of the gas is increased, an arc is generated along the gas flow path, and the movement of the cathode spot is suppressed. As a result, high-purity carbon nanotubes are synthesized at the fixed cathode spot.
[0022]
Next, a method for producing carbon nanotubes using the carbon nanotube production apparatus configured as described above will be described.
The cathode heating means 7 preheats the discharge generating portion of the carbon cathode 1 and the anode cooling means 9 cools the vicinity of the anode discharge generating portion. In this state, an arc discharge is performed by supplying an inert gas from the discharge gas supply means to the discharge generation space.
[0023]
At this time, the discharge generating portion of the carbon cathode 1 is preheated, and a temperature region where carbon nanotubes are likely to grow is formed on the surface of the carbon cathode. For this reason, with the start of arc discharge, the production of carbon nanotubes is started in this region, and as a result, the amount of carbon nanotube production increases. Here, the reason why the amount of carbon nanotubes generated in the preheated region increases is considered to be that the temperature at which the carbon nanotubes easily grow is obtained by performing arc discharge in the preheated region.
[0024]
Moreover, the anode 3 can be prevented from being overheated by the cooling by the anode cooling means 9, and excessive evaporation of the anode 3 can be suppressed. Thereby, it can suppress that the evaporated anode material adheres as an impurity to the carbon nanotube surface in which the anode material was generated, and lowers the purity. Furthermore, consumption of the anode 3 can be suppressed, and the life of the anode can be extended.
[0025]
Example 1
Hereinafter, examples of the first embodiment will be described.
The conditions of each device etc. of the present embodiment are as follows.
(1) Carbon cathode 1: plate-like carbon material (resistance value 600 μΩ · cm)
(2) Anode 3: Rod-like carbon material (3) Discharge gas: Ar gas (supplied to the anode discharge generation part)
(4) Atmospheric gas: Atmospheric atmosphere (5) Cathode heating means: YAG laser (Adjusted so that the beam irradiation diameter is substantially equal to the diameter of the discharge generating portion on the cathode surface.)
(6) Anode cooling means: water-cooled copper
Under the above conditions, an appropriate gap was provided between the plate-like carbon material and the rod-like carbon material, and an electric current was supplied from the arc discharge power source to perform an arc discharge for 1 second.
At this time, the laser output was changed to observe the plate-like carbon cathode heating temperature and the amount of carbon nanotubes produced. As a result of observation, it was confirmed that the amount of carbon nanotubes generated was increased by performing preheating of the cathode surface to 500 ° C. to 2000 ° C. only by laser irradiation before starting arc discharge.
[0027]
FIG. 2 shows the relationship between the presence or absence of heating, the heating temperature, and the carbon nanotube production state. FIG. 2 is an enlarged photograph of the central part of the cathode spot of the arc. As can be seen from FIG. 2, no carbon nanotubes were produced when preheating was not performed. It can be seen that carbon nanotubes are formed on one side of the sample preheated at 500 ° C. In addition, in the case of preheating at 2000 ° C., carbon nanotubes are generated on one side, and it can be seen that the tube grows long. Carbon nanotubes were not observed in the sample preheated at 2500 ° C. This seems to be because when the heat generated by arc discharge is added to the preheating at 2500 ° C, the cathode where the carbon nanotubes are generated is overheated, and the generated carbon nanotubes are sublimated or decomposed. The amount is significantly reduced.
[0028]
From this example, it became clear that the amount of carbon nanotube production was influenced by the cathode preheating temperature. It was also found that the preheating temperature of the carbon cathode is optimally set to 500 ° C to 2000 ° C.
[0029]
In the case where no preheating was performed in this example, no carbon nanotubes were generated, because the arc discharge time was as short as 1 second.
Therefore, if the arc discharge is performed for a long time and the temperature of the cathode discharge part rises to reach the same generation condition region as that in the case of preheating, the carbon nanotube is generated.
However, whether or not the temperature of the cathode part reaches the temperature range where the carbon nanotubes are generated varies greatly depending on the size, bulk density, specific heat, thermal conductivity, discharge conditions, etc. of the cathode carbon material. It's not easy.
On the other hand, if preheating and heating are performed as in the present invention, carbon nanotubes can be generated in a high yield without being greatly affected by these fluctuation factors.
[0030]
Embodiment 2. FIG.
FIG. 3 is a diagram for explaining the configuration of another embodiment of the present invention, and shows the basic configuration of a carbon nanotube production apparatus in the same manner as FIG. In FIG. 3, the same parts as those shown in FIG.
The carbon nanotube production apparatus of the present embodiment moves the carbon cathode 1, the anode 3, the arc power generation DC power supply 5, the cathode heating means 11, the anode cooling means 13, and the anode 3 relative to the carbon cathode 1. The moving mechanism 15 is configured.
[0031]
The moving mechanism 15 includes a carriage 19 that can travel on the rail 17 at a predetermined speed, and the anode 3 is attached to the carriage 19.
The cathode heating means 11 is composed of a high frequency induction heating device installed in the moving direction of the carriage 19 of the anode 3. The cathode heating means 11 may be installed on the anode cooling means 13 or directly on the carriage 19.
The anode cooling means 13 is the same as that in the first embodiment, and is water-cooled copper installed in the vicinity of the discharge generating portion of the anode 3.
[0032]
A method for producing carbon nanotubes using the carbon nanotube production apparatus configured as described above will be described.
The basic operation of the apparatus is the same as that of the first embodiment. The cathode heating means 11 preheats the discharge generating portion of the carbon cathode 1 and the anode cooling means 13 cools the vicinity of the discharge generating portion of the anode 3. In this state, the carriage 19 is moved at a predetermined speed, for example, 10 cm / min, while performing an arc discharge by injecting an inert gas from a discharge gas supply means (not shown) into the discharge generation space.
[0033]
According to the present embodiment, since the cathode heating means 11 is arranged in front of the anode 3, the discharge generating portion is preheated with the movement of the carriage 19, and the effect of the first embodiment described above can be obtained. At the same time, the carbon nanotubes can be continuously produced.
[0034]
In the second embodiment, the example of the carbon cathode 1 is assumed to be a flat plate or a prism, and the anode 3 moves in the direction along the surface of the carbon cathode 1.
However, the present invention is not limited to this. For example, as shown in the schematic diagram of FIG. 4, the carbon cathode 1 is rotated using a cylindrical cathode as the carbon cathode 1 and the anode 3 is moved along the axis of the cylinder. Move in the direction. At this time, both ends of the carbon cathode 1 may be connected to an AC power source to heat the entire carbon cathode 1 by self-heating due to resistance heating. In this way, preheating and heating of the carbon cathode 1 can be realized with a simple device.
[0035]
However, when the cathode material becomes large, in order to preheat and heat the entire cathode by resistance heating, not only the power source is increased, but also the heat loss of the cathode material due to radiation is large and the amount of electricity used is increased. Invite.
Therefore, in such a case, as shown in FIG. 5, a laser oscillator may be installed in the vicinity of the anode 3 to partially heat the cathode spot of the arc discharge or the front of the cathode spot.
Thus, the local heating is sufficient because the generation of carbon nanotubes affects only the temperature of the discharge generating portion of the cathode material. As another example of the local heating heat source, arc discharge by an electrode different from the electrode for generating the carbon nanotube may be considered.
[0036]
(Example 2)
Hereinafter, examples of the second embodiment will be described.
The conditions of this example are as follows.
(1) Carbon cathode 1: Flat carbon material (2) Anode 3: Rod-shaped carbon material (3) Discharge gas: Ar gas (supplied to the anode discharge generation section)
(4) Atmospheric gas: Atmospheric atmosphere (5) Cathode heating means: High frequency induction heating device (interval with carbon cathode: 4 mm)
(6) Anode cooling means: Water-cooled copper (7) Bogie 19 Movement speed: 10 cm / min
[0037]
When heating was performed with the starting frequency of the high-frequency induction heating apparatus set to 10 kHz under the above conditions, the cathode temperature increased to 800 ° C. only by high-frequency induction heating.
In this state, when Ar gas is injected into the discharge space from the discharge gas supply device and arc discharge is generated between the anode and the cathode, high-density and high-purity carbon nanotubes are generated.
[0038]
In this example, the discharge time in the atmosphere was 5 minutes. However, when the anode was not cooled, the consumption was so severe that continuous discharge for 2 minutes or more was impossible. On the other hand, when the anode was cooled with water, it was consumed somewhat immediately after the start of discharge.
[0039]
When observing the surface of the completed carbon nanotubes, it was observed that the amount of adhering impurities decreased compared to the case where the anode was not cooled. FIG. 6 is an enlarged photograph of the central part of the arc cathode spot. From this photograph, the difference in the impurity adhesion state depending on whether or not the anode is cooled is noticeable.
[0040]
From the results of this example, it was confirmed that most of the carbon impurities adhering to and depositing on the carbon nanotubes generated in the cathode discharge generating portion are flying objects from the anode. Therefore, by cooling the anode, it is possible not only to suppress the anode consumption more than necessary, but also to suppress the accumulation of scattered matter from the anode that becomes impurities on the carbon nanotubes generated on the cathode surface, as well as the length of the anode. It was proved that the life could be improved.
[0041]
In the above embodiment, the carbon material is used as the anode. However, the anode of the present invention is not limited to the carbon material, and may be a water-cooled copper electrode.
[0042]
【The invention's effect】
As described above, in the present invention, since the entire cathode carbon material or the arc discharge part of the cathode carbon material is preheated and then arc discharge is performed between the anode and the anode, the yield of carbon nanotubes can be obtained with a simple device. Can be more.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a configuration according to an embodiment of the present invention.
FIG. 2 is a scanning electron microscope (SEM) photograph of the central portion of the cathode deposit obtained by the carbon nanotube manufacturing method according to one embodiment of the present invention.
FIG. 3 is an explanatory diagram of a configuration of another embodiment of the present invention.
FIG. 4 is an explanatory diagram of another aspect of another embodiment of the present invention.
FIG. 5 is an explanatory diagram of another aspect of another embodiment of the present invention.
FIG. 6 is a scanning electron microscope (SEM) photograph of the central part of the cathode deposit obtained by the carbon nanotube manufacturing method according to another embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Carbon cathode 3 Anode 5 Arc discharge power supply 7, 11 Cathode heating means 9, 13 Anode cooling means 15 Moving mechanism 19 Carriage

Claims (8)

A carbon nanotube production method for synthesizing a carbon nanotube by performing a direct current arc discharge using a cathode made of a carbon material,
A method for producing carbon nanotubes , comprising preheating an entire cathode carbon material or an arc discharge portion of the cathode carbon material, performing arc discharge between the anode and the anode, and cooling the anode .   2. The method for producing carbon nanotubes according to claim 1, wherein direct current arc discharge is performed while moving the relative position of the cathode and the anode.   3. The method for producing carbon nanotubes according to claim 1, wherein the whole of the cathode carbon material or the arc discharge part of the cathode carbon material is heated by a heating means different from the arc discharge during the arc discharge.   The method for producing a carbon nanotube according to any one of claims 1 to 3, wherein the preheating temperature is 500C to 2000C. The method for producing carbon nanotubes according to any one of claims 1 to 4, wherein the preheating method is high-frequency induction heating, arc discharge by another electrode, heating by laser irradiation, or energization heating by another power source. A cathode electrode made of a carbon material;
An anode electrode disposed opposite to the cathode electrode at a predetermined interval;
An arc discharge power source connected to the anode electrode and the cathode electrode to cause arc discharge between these electrodes;
Heating means for heating the entire cathode electrode or an arc discharge portion of the cathode electrode;
An apparatus for producing carbon nanotubes, comprising: an anode cooling means for cooling the anode electrode . 7. The carbon nanotube production apparatus according to claim 6, further comprising moving means for relatively moving the cathode electrode and the anode electrode. The carbon nanotube manufacturing apparatus according to claim 6 or 7 , wherein the heating means is a high-frequency induction heating apparatus, an arc discharge apparatus using another electrode, or an energization heating apparatus using a laser or another power source.

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